Many of the existing military aircraft are equipped with convergent divergent nozzles. These can optimize the thrust for different flying conditions by varying the nozzle throat and exit area.
The manoeuvering capability of the aircraft together with the flying envelope can be enhanced by providing the aircraft with the capability of vectoring the thrust by introducing a component perpendicular to the engine axis. Thrust vectoring can be achieved with a change in the geometry of the divergent nozzle section with the convergent section remaining axisymmetric.
One of the possible arrangements for the divergent sections consists of a number of master petals positioned circumferentially around a conical section. Slave petals are positioned closing the gaps between each two of the master petals on the internal side of the conical surface. Engine gas pressure pushes the slave petals against the master petals providing adequate sealing.
The position of the slave petals between master petals must avoid disengagement or circumstance in which the sides of a master and slave petal cross allowing a gas exit. Slave petals must also be capable to deflect through flexion and/or torsion to adapt their sides to the gas side surfaces of the master petals, guaranteeing proper sealing.
The position of the master divergent petals can be determined by an actuation system consisting of hydraulic actuators, an actuation ring and different struts that connect each of the master divergent petals to the actuation ring. For a given position of the actuators and throat area the opening and vectoring degree of the divergent section is determined.
The slave petals are positioned radially by the engine gas pressure and the reaction against the master petals. The circumferential and axial position of each petal is determined by a centering mechanism that can be connected to the convergent section and the adjacent master petals. The mentioned mechanism must guarantee a centered position for both axisymmetric and vectored configurations. The system must also be compatible with the torsion and flexion of the slave petal.
Hangers must avoid the displacement of the slave petal away from the master petals when the gas pressure is less than the outer cavity pressure on the air side of the petal. This condition is encountered for large divergence angles at determined points of the flying envelope.